On commercial aircraft with in-flight catering services, it is common for one or more of the galleys installed on the aircraft to be “wet,” i.e. to have a water supply (potable water), water drainage (waste water), and on occasion water used in a waste disposal unit (foul water—post use). The potable water is supplied under pressure to the galley, while gravity, which can be assisted by a vacuum, is used in water drainage and waste disposal. The potable water is used for drinking water, beverage making and cooking (e.g., steam ovens, rice boilers, etc.), and therefore has to meet safety criteria that make it fit for human consumption. That is, potable water must meet certain minimum health and safety standards, and then it is generally filtered to improve taste, smell and to remove bacteria in accordance with airline policy. The aircraft galley plumbing system encompasses all aspects of water usage on a galley, its associated hardware, components and galley equipment which either consume or facilitate water handling.
All galley plumbing systems must pass design and regulatory requirements specified by the aircraft manufacturers and must undergo testing to ensure that the potable, waste and foul water systems are fully functional and remain separated to ensuring no cross contamination. Also, when the aircraft shuts down on completion of a flight, or for longer periods of storage or maintenance, all of the plumbing systems must be capable of draining completely within a specified time. Any residual water that could potentially become contaminated must be purged from the aircraft galley plumbing system. Therefore, the system allows air contained within the plumbing system pipes, hoses, and components to be displaced by water during the filling cycle (with the air vented out), and air replaces the water during the drainage/purge cycle (air vented in) allowing rapid water displacement.
At the resumption of service, the potable water supply circuit must be capable of being filled automatically without manual assistance, and all sections that may potentially trap air must be capable of self-venting. An important consideration to this goal is that the pressure varies depending on the aircraft and design.
From a safety standpoint, the plumbing system must also prevent hot water backflow to the faucets from the galley inserts (GAINs). Moreover, hydraulic pressure reduction is desirable to improve flow and increase water consumption capacity.